<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="fn(1)">
<input type="button" value="减" onclick="fn(2)">
<input type="button" value="乘" onclick="fn(3)">
<input type="button" value="除" onclick="fn(4)">
<div>结果：0</div>

<script>
    let i1=document.querySelector("#i1");
    let i2=document.querySelector("#i2");
    let d=document.querySelector("div");
    function fn(x) {
        if (isNaN(i1.value)||isNaN(i2.value)){
            d.innerText("输入错误");
            return;
        }
        switch (x) {
            case 1: d.innerText="结果："+(parseFloat(i1.value)+parseFloat(i2.value)); break;
            case 2: d.innerText="结果："+(parseFloat(i1.value)-parseFloat(i2.value)); break;
            case 3: d.innerText="结果："+(parseFloat(i1.value)*parseFloat(i2.value)); break;
            case 4: d.innerText="结果："+(parseFloat(i1.value)/parseFloat(i2.value)); break;
        }

    }


</script>

</body>
</html>